@WTP
Different laws in different states is exactly why we have separate Bar Exams for each state. One day National law is tested, day two, state law is tested.
I am admitted in CT, MA (where I went to Law School), NY and FL. I am old enough that after practicing in CT for 5 years, all I had to do was pay my fee to NY, drive to Albany and be sworn in. Nowadays, I’d have to take and pass the NYS Bar Exam. I took and passed the other exams. I am also admitted to the Federal Bar for my District.
That said, No one knows every law on the books in their state. Lawyers and Judges tend to keep up to speed on the areas of their practice. Otherwise they look things up or have clerks and paralegals research and report results. I was in court this morning with a Judge in Housing Session, Superior Court. He had just been transferred in after 5 years in the Family Law Division. In one 30 minute session, he stopped and referred to the Connecticut General Statutes (on line version) 4 times before rendering a decision.